1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine, which controls the start and stop of the internal combustion engine in a vehicle driven by a driving force output from the internal combustion engine, and provided with a vehicular air conditioning device that conditions the air in a vehicle cabin using a coolant for the internal combustion engine as a heat source.
2. Description of the Related Art
A vehicular air conditioning device cools air using the evaporator of a refrigeration-cycle system, and heats the air using a heater core where an engine coolant for an internal combustion engine circulates. In this manner, the air conditioning device conditions the air. Then, the air conditioning device supplies the conditioned air into a vehicle cabin to cool or heat the vehicle cabin.
In recent years, vehicles in which a so-called economy-running control, such as an idling-stop control, is executed have become widely available. In the idling-stop control, when a predetermined engine stop condition is satisfied, an engine stops. When the engine is stopped, and a predetermined engine start condition (engine restart condition) is satisfied, the engine starts. Thus, for example, by executing the idling-stop control to stop the engine when the vehicle is stopped, fuel efficiency is improved, emission gas is reduced, and vibration and noise are suppressed when the vehicle is stopped.
When the air conditioner is heating the vehicle cabin, and the engine stops, the temperature of the engine coolant decreases. Further, the heating capacity of the air conditioner decreases due to the decrease in the temperature of the engine coolant. As a result, the air in the vehicle cabin is not conditioned (heated) to a desired level.
In vehicles, when the temperature of the engine coolant decreases, the engine generally is started to maintain the temperature of the engine coolant in a predetermined range. This suppresses the decrease in the heating capacity resulting from the decrease in the temperature of the engine coolant. In other words, the engine is driven and stopped based on the temperature of the engine coolant, that is, based on whether the temperature of the engine coolant is above a predetermined threshold value.
However, when the engine is started to suppress the decrease in the temperature of the engine coolant, the effect of improving the fuel efficiency and reducing emission gas is less significant. Further, although vibration, noise, and the like caused by the engine are suppressed in recent vehicles, occupants in the vehicles still feel noise and vibration when the vehicles are stopped. Particularly when the engine is repeatedly driven and stopped due to the changes in the temperature of the engine coolant, the occupants are discomforted by the vibration and noise.
Thus, Japanese Patent Application Publication No. 2002-211238 (JP-A-2002-211238) describes that there is a certain difference between the threshold value of the coolant temperature at which the engine restarts when the coolant temperature decreases, and the threshold value of the coolant temperature at which the engine automatically stops when the coolant temperature increases after the engine starts. This reduces the possibility that the engine repeatedly and frequently stops and restarts.
However, in the above-described case where there is the certain difference between the threshold value at which the engine restarts and the threshold value at which the engine stops, the engine still needs to restart to maintain the required heating capacity of the air conditioner when the coolant temperature decreases. Further, when the difference is set to maintain the required heating capacity, the engine operates for a long period of time.